Question on modelling a sword
That would depend on what you intended its use for.

If for the sake of mock up design then either option is fine. I'd recommend trying whichever you're less comfortable with if only to test your ability with blender.

If you intend to break or damage the sword at some later point, then keeping it seperate is more practical. 

IF seperate - You should adjust the contours of the grip so that they match the contours of the gaurd (utilizing Edge/Vertex Selection)



(You should add the tang too(B) if that is the case)